Paper webs made from cellulosic fibers are used in consumer products such as paper towels, toilet tissue, and facial tissue. Multiple ply paper structures are well known in the art. Such multiple ply structures have two or more plies which are positioned in face to face relationship and joined together. Each ply can be formed from a paper web. A paper web can have one or more layers as it is formed on a paper machine, as is also well known in the art.
The individual plies of a multiple ply paper structure can be joined in any number of suitable ways, including adhesive bonding or mechanical bonding, such as by embossing. Frequently, plies are embossed for aesthetic reasons, to provide space between adjacent plies, and to connect adjacent plies in face to face relationship.
Examples of multiple ply paper structures are shown in the following references: U.S. Pat. No. 3,650,882 issued March, 1972 to Thomas; U.S. Pat. No. 4,469,735 issued September, 1984 to Trokhan; and U.S. Pat. No. 3,953,638 issued April 1976 to Kemp. The following references disclose embossing or embossed products or multiple ply paper products: U.S. Pat. No. 5,490,902 issued Feb. 13, 1996 to Shulz; U.S. Pat. No. 5,468,323 issued November 1995 to McNeil and commonly assigned; U.S. Pat. No. 4,300,981 issued November 1981 to Carstens; U.S. Pat. No. 3,414,459 issued Dec. 3, 1968 to Wells and commonly assigned; U.S. Pat. No. 3,547,723 issued Dec. 15, 1970 to Gresham; U.S. Pat. No. 3,556,907 issued Jan. 19, 1971 to Nystrand; U.S. Pat. No. 3,708,366 issued Jan. 2, 1973 to Donnelly; U.S. Pat. No. 3,738,905 issued Jun. 12, 1973 to Thomas; U.S. Pat. No. 3,867,225 issued Feb. 18, 1975 to Nystrand and U.S. Pat. No. 4,483,728 issued Nov. 20, 1984 to Bauernfeind. Commonly assigned U.S. Pat. No. Des. 239,137 issued Mar. 9, 1976 to Appleman illustrates an emboss pattern found on commercially successful paper toweling.
It is generally understood that a multiple ply structure can have an absorbent capacity greater than the sum of the absorbent capacities of the individual single plies which make up the multiple ply structure. Above referenced U.S. Pat. No. 3,650,882 to Thomas discloses a three ply product which is said to have a water absorbtion capacity which is more than double that of two ply towels of similar furnish, and which is said to have an absorbent capacity which is greater than would be expected from a simple consideration of the additional amount of material in a three ply structure.
However, comparison of the absorbent capacity of a multiple ply structure to the absorbent capacities of single ply paper structures, or other multiple ply paper structures having fewer plies, is not especially helpful in judging the performance of the multiple ply product. The absorbent capacity gained by adding an additional ply is generally greater than absorbent capacity held within the added ply. This difference is due, at least in part, to the inter-ply storage space created by the addition of an extra ply.
A heterogeneous n ply product having plies obtained from different types of substrates is normally expected to have an absorbent capacity which is no greater than the arithmatic mean of the absorbent capacities measured for the homogeneous n ply structures formed from the different substrates. For instance, a heterogeneous two ply tissue product has a first ply formed from a first type of paper substrate and a second ply formed from a second, different type of paper substrate. The absorbent capacity of such a heterogeneous two ply product is generally expected to be less than or equal to the arithmatic mean of the absorbent capacities measured for 1) a homogeneous two ply structure formed from two plies of the first substrate and 2) a homogeneous two ply structure formed from two plies of the second substrate.
Above referenced U.S. Pat. No. 4,469,735 discloses extensible multi-ply tissue paper products. The products of U.S. Pat. No. 4,469,735 are said to have synergistically high liquid absorbency by virtue of at least two plies of the product having sufficiently different stress/strain properties. However, it is desirable to be able to provide improved absorbency without the need to impart different stress/strain properties to different plies.
Accordingly, one object of the present invention is to provide a multiple ply paper structure having improved absorbent properties.
Another object of the present invention is to provide a multiple ply paper structure which achieves a higher absorbent capacity and rate than anticipated with respect to other paper structures having the same number of plies.
Another object of the present invention is to provide a multiple ply paper structure having plies with different texture values and calipers.
Another object of the present invention is to provide a multiple ply paper structure having one or more plies having discrete, low density regions dispersed in a continuous network region.